MChem Master of Chemistry Master of Chemistry: Analytical Chemistry 3 — Questions and Answers
Question 1: Which titration method exploits the formation of a colored metal-indicator complex that is displaced by EDTA at the equivalence point?
- Argentometric titration
- Complexometric (chelatometric) titration (Correct answer)
- Redox titration with KMnO4
- Acid-base titration with phenolphthalein
Correct answer: Complexometric (chelatometric) titration
Complexometric titrations use metal indicators like Eriochrome Black T, which form colored complexes with metal ions that EDTA displaces at the endpoint.
Question 2: In atomic absorption spectroscopy (AAS), the hollow cathode lamp (HCL) is used because it emits:
- Broad-band continuum radiation for background correction
- Narrow-line radiation matching the analyte's absorption wavelength (Correct answer)
- UV radiation to photoionize the analyte
- Infrared radiation to excite vibrational modes
Correct answer: Narrow-line radiation matching the analyte's absorption wavelength
The HCL emits narrow atomic lines of the same element as its cathode, perfectly matching the absorption profile of the analyte atoms.
Question 3: What is the primary advantage of using a standard addition method over external calibration in atomic spectrometry?
- It requires fewer standards to prepare
- It compensates for matrix effects that alter the analytical signal (Correct answer)
- It extends the linear dynamic range of the detector
- It eliminates the need for a blank correction
Correct answer: It compensates for matrix effects that alter the analytical signal
Standard addition compensates for matrix-matched suppression or enhancement because the standards experience the same matrix as the unknown sample.
Question 4: In cyclic voltammetry, what information is obtained from the ratio of the cathodic to anodic peak currents (i_pc/i_pa)?
- The diffusion coefficient of the analyte
- The reversibility of the redox process (Correct answer)
- The formal reduction potential
- The electron transfer rate constant
Correct answer: The reversibility of the redox process
For a reversible one-electron process, i_pc/i_pa = 1; deviations indicate chemical reactions coupled to electron transfer (EC or CE mechanisms).
Question 5: Which separation mode in capillary electrophoresis is used specifically to separate neutral (uncharged) analytes?
- Capillary zone electrophoresis (CZE)
- Micellar electrokinetic chromatography (MEKC) (Correct answer)
- Capillary isoelectric focusing (CIEF)
- Capillary gel electrophoresis (CGE)
Correct answer: Micellar electrokinetic chromatography (MEKC)
MEKC incorporates surfactant micelles as a pseudostationary phase that partitions neutral analytes, enabling their separation by electrophoresis.
Question 6: In X-ray fluorescence (XRF) spectrometry, the energy of the emitted characteristic X-ray is determined by:
- The incident X-ray beam intensity
- The binding energy difference between the electron shells involved in the transition (Correct answer)
- The atomic mass of the element
- The crystal lattice spacing of the detector
Correct answer: The binding energy difference between the electron shells involved in the transition
XRF emission energy equals the difference in binding energies of the two electron shells (e.g., K and L shells) involved in the electronic transition.
Question 7: Which parameter in a validated analytical method describes the ability to detect small, deliberate changes in method variables without affecting results?
- Selectivity
- Robustness (ruggedness) (Correct answer)
- Linearity
- Repeatability
Correct answer: Robustness (ruggedness)
Robustness measures the method's resistance to small, deliberate variations in parameters such as pH, temperature, or mobile phase composition.
MChem Master of Chemistry Master of Chemistry: Analytical Chemistry 3
Which titration method exploits the formation of a colored metal-indicator complex that is displaced by EDTA at the equivalence point?